Molecular genetics of acute myeloid leukaemia

Transcriptional Landscape of CUT-Class Homeobox Genes in Blastic Plasmacytoid Dendritic Cell Neoplasm

Homeobox genes encode developmental transcription factors regulating tissue-specific differentiation processes and drive cancerogenesis when deregulated. Dendritic cells (DCs) are myeloid immune cells occurring as two types, either conventional or plasmacytoid DCs. Recently, we showed that the expression of NKL-subclass homeobox gene VENTX is restricted to conventional DCs, regulating developmental genes. Here, we identified and investigated homeobox genes specifically expressed in plasmacytoid DCs (pDCs) and derived blastic plasmacytoid dendritic cell neoplasm (BPDCN). We analyzed gene expression data, performed RQ-PCR, protein analyses by Western blot and immuno-cytology, siRNA-mediated knockdown assays and subsequent RNA-sequencing and live-cell imaging. Screening of public gene expression data revealed restricted activity of the CUT-class homeobox gene CUX2 in pDCs. An extended analysis of this homeobox gene class in myelopoiesis showed that additional CUX2 activity was restricted to myeloid progenitors, while BPDCN patients aberrantly expressed ONECUT2, which remained silent in the complete myeloid compartment. ONECUT2 expressing BPDCN cell line CAL-1 served as a model to investigate its regulation and oncogenic activity. The ONECUT2 locus at 18q21 was duplicated and activated by IRF4, AUTS2 and TNF-signaling and repressed by BMP4-, TGFb- and IL13-signalling. Functional analyses of ONECUT2 revealed the inhibition of pDC differentiation and of CDKN1C and CASP1 expression, while SMAD3 and EPAS1 were activated. EPAS1 in turn enhanced survival under hypoxic conditions which thus may support dendritic tumor cells residing in hypoxic skin lesions. Collectively, we revealed physiological and aberrant activities of CUT-class homeobox genes in myelopoiesis including pDCs and in BPDCN, respectively. Our data may aid in the diagnosis of BPDCN patients and reveal novel therapeutic targets for this fatal malignancy.

The Hematopoietic TALE-Code Shows Normal Activity of IRX1 in Myeloid Progenitors and Reveals Ectopic Expression of IRX3 and IRX5 in Acute Myeloid Leukemia

Homeobox genes encode transcription factors that control basic developmental decisions. Knowledge of their hematopoietic activities casts light on normal and malignant immune cell development. Recently, we constructed the so-called lymphoid TALE-code that codifies expression patterns of all active TALE class homeobox genes in early hematopoiesis and lymphopoiesis. Here, we present the corresponding myeloid TALE-code to extend this gene signature, covering the entire hematopoietic system. The collective data showed expression patterns for eleven TALE homeobox genes and highlighted the exclusive expression of IRX1 in megakaryocyte-erythroid progenitors (MEPs), implicating this TALE class member in a specific myeloid differentiation process. Analysis of public profiling data from acute myeloid leukemia (AML) patients revealed aberrant activity of IRX1 in addition to IRX3 and IRX5, indicating an oncogenic role for these TALE homeobox genes when deregulated. Screening of RNA-seq data from 100 leukemia/lymphoma cell lines showed overexpression of IRX1, IRX3, and IRX5 in megakaryoblastic and myelomonocytic AML cell lines, chosen as suitable models for studying the regulation and function of these homeo-oncogenes. Genomic copy number analysis of IRX-positive cell lines demonstrated chromosomal amplification of the neighboring IRX3 and IRX5 genes at position 16q12 in MEGAL, underlying their overexpression in this cell line model. Comparative gene expression analysis of these cell lines revealed candidate upstream factors and target genes, namely the co-expression of GATA1 and GATA2 together with IRX1, and of BMP2 and HOXA10 with IRX3/IRX5. Subsequent knockdown and stimulation experiments in AML cell lines confirmed their activating impact in the corresponding IRX gene expression. Furthermore, we demonstrated that IRX1 activated KLF1 and TAL1, while IRX3 inhibited GATA1, GATA2, and FST. Accordingly, we propose that these regulatory relationships may represent major physiological and oncogenic activities of IRX factors in normal and malignant myeloid differentiation, respectively. Finally, the established myeloid TALE-code is a useful tool for evaluating TALE homeobox gene activities in AML.

First report from a single center retrospective study in Kazakhstan on acute myeloid leukemia treatment outcomes

Acute myeloid leukemia (AML) is the most common hematological malignancy in adults. In the last decade, internationally approved AML treatment guidelines, including hematopoietic stem cell transplantation are widely used in Kazakhstan. The categorization of acute myeloid leukemia was done according to the French-American British classification. The prognosis of patients at the time of diagnosis was determined by cytogenetic tests following the guidelines of the European LeukemiaNet. The overall survival and event-free survival were analyzed using the Kaplan-Meier method, and hazard ratios were defined with Cox regression. In total, 398 patients with AML were treated in the National Research Oncology Center between 2010 and 2020. The mean age was 38.3 years. We found a correlation between ethnicity, cytogenetic group, white blood cell count, and treatment approaches with overall and event-free survival. There was a significantly longer OS in a cytogenetic group with a good prognosis compared with intermediate and poor prognosis. The median survival time in the group with a good prognosis was 43 months, 23 months in the intermediate group (p = 0.7), and 12 months in the poor prognosis group (p = 0.016). There was a significantly longer OS for the group of patients who received hematopoietic stem cell transplantation (HSCT), 52 months versus 10 months in the group who received chemotherapy only, p-value < 0.0001. Prognostic factors, such as cytogenetic group, initial WBC count, and treatment approaches are significantly associated with patient survival. Our study data were consistent with the most recent studies, available in the literature adjusted for the population in question.

FLT3 Gene Mutation in Acute Myeloid Leukemia: Correlation with Hematological, Immunophenotypic, and Cytogenetic Characteristics

Introduction In acute myeloid leukemia (AML), FMS-like tyrosine kinase 3-internal tandem duplication (FLT3-ITD) is a common driver mutation associated with high tumor burden and poor prognosis. This mutation is common in normal karyotype AML and such patients have high leukocyte count. The presence of this mutation can be predicted by certain hematological and immunophenotypic characteristics in day-to-day practice.

Objective This study was undertaken to assess the strength of association between FLT3 gene mutation and hematological and immunophenotypic characteristics.

Materials and Methods Morphological, hematological, immunophenotypic, and cytogenetic characteristics of FLT3 mutations recorded in 424 patients of AML in adults and children between 2016 and 2019 in a tertiary care cancer center in Western India. Blasts were classified according to French-American-British method. Tumor burden was assessed by serum lactate dehydrogenase (LDH) levels, leucocyte count, and peripheral smear blast percentage.

Results Out of 424 cases, FLT3-ITD and FLT3-tyrosine kinase domain mutation were found in 72 and 25 AML patients, respectively. Patients with FLT3 mutation had high tumor burden, characterized by high leukocyte count (p < 0.001), peripheral blood (p = 0.01) and bone marrow (p = 0.03) blast percentage, and high serum LDH (mean 777.8 vs. 586; p = 0.10) compared with FLT3-negative patients. They also featured high platelet count (p < 0.001). Morphological, immunophenotypic, and cytogenetic characteristics also have been presented in the study.

Conclusion Observations of the study suggest the presence of definitive hematological and immunophenotypic characteristics along with raised serum LDH levels serve as surrogate markers and indicators of FLT3 mutation in AML patients.

Formaldehyde-induced hematopoietic stem and progenitor cell toxicity in mouse lung and nose

Formaldehyde (FA), an economically important and ubiquitous chemical, has been classified as a human carcinogen and myeloid leukemogen. However, the underlying mechanisms of leukemogenesis remain unclear. Unlike many classical leukemogens that damage hematopoietic stem/progenitor cells (HSC/HPC) directly in the bone marrow, FA-as the smallest, most reactive aldehyde-is thought to be incapable of reaching the bone marrow through inhalation exposure. A recent breakthrough study discovered that mouse lung contains functional HSC/HPC that can produce blood cells and travel bi-directionally between the lung and bone marrow, while another early study reported the presence of HSC/HPC in rat nose. Based on these findings, we hypothesized that FA inhalation could induce toxicity in HSC/HPC present in mouse lung and/or nose rather than in the bone marrow. To test this hypothesis, we adapted a commercially available protocol for culturing burst-forming unit-erythroid (BFU-E) and colony-forming unit-granulocyte, macrophage (CFU-GM) colonies from bone marrow and spleen to also enable culture of these colonies from mouse lung and nose, a novel application of this assay. We reported that in vivo exposure to FA at 3 mg/m3 or ex vivo exposure up to 400 µM FA decreased the formation of both colony types from mouse lung and nose as well as from bone marrow and spleen. These findings, to the best of our knowledge, are the first empirically to show that FA exposure can damage mouse pulmonary and olfactory HSC/HPC and provide potential biological plausibility for the induction of leukemia at the sites of entry rather than the bone marrow.

Dnmt3a loss and Idh2 neomorphic mutations mutually potentiate malignant hematopoiesis

Mutations in the epigenetic regulators DNMT3A and IDH1/2 co-occur in patients with acute myeloid leukemia and lymphoma. In this study, these 2 epigenetic mutations cooperated to induce leukemia. Leukemia-initiating cells from Dnmt3a-/- mice that express an IDH2 neomorphic mutant have a megakaryocyte-erythroid progenitor-like immunophenotype, activate a stem-cell-like gene signature, and repress differentiated progenitor genes. We observed an epigenomic dysregulation with the gain of repressive H3K9 trimethylation and loss of H3K9 acetylation in diseased mouse bone marrow hematopoietic stem and progenitor cells (HSPCs). HDAC inhibitors rapidly reversed the H3K9 methylation/acetylation imbalance in diseased mouse HSPCs while reducing the leukemia burden. In addition, using targeted metabolomic profiling for the first time in mouse leukemia models, we also showed that prostaglandin E2 is overproduced in double-mutant HSPCs, rendering them sensitive to prostaglandin synthesis inhibition. These data revealed that Dnmt3a and Idh2 mutations are synergistic events in leukemogenesis and that HSPCs carrying both mutations are sensitive to induced differentiation by the inhibition of both prostaglandin synthesis and HDAC, which may reveal new therapeutic opportunities for patients carrying IDH1/2 mutations.

CCAAT enhancer binding protein alpha (CEBPA) biallelic acute myeloid leukaemia: cooperating lesions, molecular mechanisms and clinical relevance

Recent advances in sequencing technologies have allowed for the identification of recurrent mutations in acute myeloid leukaemia (AML). The transcription factor CCAAT enhancer binding protein alpha (CEBPA) is frequently mutated in AML, and biallelic CEBPA-mutant AML was recognised as a separate disease entity in the recent World Health Organization classification. However, CEBPA mutations are co-occurring with other aberrations in AML, and together these lesions form the clonal hierarchy that comprises the leukaemia in the patient. Here, we aim to review the current understanding of co-occurring mutations in CEBPA-mutated AML and their implications for disease biology and clinical outcome. We will put emphasis on patterns of cooperation, how these lesions cooperate with CEBPA mutations and the underlying potential molecular mechanisms. Finally, we will relate this to patient outcome and future options for personalised medicine.

Analysis of the Mechanisms of Action of Naphthoquinone-Based Anti-Acute Myeloid Leukemia Chemotherapeutics

Acute myeloid leukemia (AML) is a neoplastic disorder resulting from clonal proliferation of poorly differentiated immature myeloid cells. Distinct genetic and epigenetic aberrations are key features of AML that account for its variable response to standard therapy. Irrespective of their oncogenic mutations, AML cells produce elevated levels of reactive oxygen species (ROS). They also alter expression and activity of antioxidant enzymes to promote cell proliferation and survival. Subsequently, selective targeting of redox homeostasis in a molecularly heterogeneous disease, such as AML, has been an appealing approach in the development of novel anti-leukemic chemotherapeutics. Naphthoquinones are able to undergo redox cycling and generate ROS in cancer cells, which have made them excellent candidates for testing against AML cells. In addition to inducing oxidative imbalance in AML cells, depending on their structure, naphthoquinones negatively affect other cellular apparatus causing neoplastic cell death. Here we provide an overview of the anti-AML activities of naphthoquinone derivatives, as well as analysis of their mechanism of action, including induction of reduction-oxidation imbalance, alteration in mitochondrial transmembrane potential, Bcl-2 modulation, initiation of DNA damage, and modulation of MAPK and STAT3 activity, alterations in the unfolded protein response and translocation of FOX-related transcription factors to the nucleus.

NPM1c alters FLT3-D835Y localization and signaling in acute myeloid leukemia

Activating mutations in FMS-like tyrosine kinase receptor-3 (FLT3) and Nucleophosmin-1 (NPM1) are most frequent alterations in acute myeloid leukemia (AML), and are often coincidental. The mutational status of NPM1 has strong prognostic relevance to patients with point mutations of the FLT3 tyrosine kinase domain (TKD), but the biological mechanism underlying this effect remains unclear. In the present study, we investigated the effect of the coincidence of NPM1c and FLT3-TKD. Although expression of FLT3-TKD is not sufficient to induce a disease in mice, coexpression with NPM1c rapidly leads to an aggressive myeloproliferative disease in mice with a latency of 31.5 days. Mechanistically, we could show that FLT3-TKD is able to activate the downstream effector molecule signal transducer and activator of transcription 5 (STAT5) exclusively in the presence of mutated NPM1c. Moreover, NPM1c alters the cellular localization of FLT3-TKD from the cell surface to the endoplasmic reticulum, which might thereby lead to the aberrant STAT5 activation. Importantly, aberrant STAT5 activation occurs not only in primary murine cells but also in patients with AML with combined FLT3-TKD and NPM1c mutations. Thus, our data indicate a new mechanism, how NPM1c mislocalizes FLT3-TKD and changes its signal transduction ability.

Targeting Oncogenic Signaling in Mutant FLT3 Acute Myeloid Leukemia: The Path to Least Resistance

The identification of recurrent driver mutations in genes encoding tyrosine kinases has resulted in the development of molecularly-targeted treatment strategies designed to improve outcomes for patients diagnosed with acute myeloid leukemia (AML). The receptor tyrosine kinase FLT3 is the most commonly mutated gene in AML, with internal tandem duplications within the juxtamembrane domain (FLT3-ITD) or missense mutations in the tyrosine kinase domain (FLT3-TKD) present in 30–35% of AML patients at diagnosis. An established driver mutation and marker of poor prognosis, the FLT3 tyrosine kinase has emerged as an attractive therapeutic target, and thus, encouraged the development of FLT3 tyrosine kinase inhibitors (TKIs). However, the therapeutic benefit of FLT3 inhibition, particularly as a monotherapy, frequently results in the development of treatment resistance and disease relapse. Commonly, FLT3 inhibitor resistance occurs by the emergence of secondary lesions in the FLT3 gene, particularly in the second tyrosine kinase domain (TKD) at residue Asp835 (D835) to form a ‘dual mutation’ (ITD-D835). Individual FLT3-ITD and FLT3-TKD mutations influence independent signaling cascades; however, little is known about which divergent signaling pathways are controlled by each of the FLT3 specific mutations, particularly in the context of patients harboring dual ITD-D835 mutations. This review provides a comprehensive analysis of the known discrete and cooperative signaling pathways deregulated by each of the FLT3 specific mutations, as well as the therapeutic approaches that hold the most promise of more durable and personalized therapeutic approaches to improve treatments of FLT3 mutant AML.

Turning Stem Cells Bad: Generation of Clinically Relevant Models of Human Acute Myeloid Leukemia through Gene Delivery- or Genome Editing-Based Approaches

Acute myeloid leukemia (AML), the most common acute leukemia in the adult, is believed to arise as a consequence of multiple molecular events that confer on primitive hematopoietic progenitors unlimited self-renewal potential and cause defective differentiation. A number of genetic aberrations, among which a variety of gene fusions, have been implicated in the development of a transformed phenotype through the generation of dysfunctional molecules that disrupt key regulatory mechanisms controlling survival, proliferation, and differentiation in normal stem and progenitor cells. Such genetic aberrations can be recreated experimentally to a large extent, to render normal hematopoietic stem cells "bad", analogous to the leukemic stem cells. Here, we wish to provide a brief outline of the complementary experimental approaches, largely based on gene delivery and more recently on gene editing, employed over the last two decades to gain insights into the molecular mechanisms underlying AML development and progression and on the prospects that their applications offer for the discovery and validation of innovative therapies.

Dysregulation of haematopoietic stem cell regulatory programs in acute myeloid leukaemia

Haematopoietic stem cells (HSC) are situated at the apex of the haematopoietic differentiation hierarchy, ensuring the life-long supply of mature haematopoietic cells and forming a reservoir to replenish the haematopoietic system in case of emergency such as acute blood loss. To maintain a balanced production of all mature lineages and at the same time secure a stem cell reservoir, intricate regulatory programs have evolved to control multi-lineage differentiation and self-renewal in haematopoietic stem and progenitor cells (HSPCs). Leukaemogenic mutations commonly disrupt these regulatory programs causing a block in differentiation with simultaneous enhancement of proliferation. Here, we briefly summarize key aspects of HSPC regulatory programs, and then focus on their disruption by leukaemogenic fusion genes containing the mixed lineage leukaemia (MLL) gene. Using MLL as an example, we explore important questions of wider significance that are still under debate, including the importance of cell of origin, to what extent leukaemia oncogenes impose specific regulatory programs and the relevance of leukaemia stem cells for disease development and prognosis. Finally, we suggest that disruption of stem cell regulatory programs is likely to play an important role in many other pathologies including ageing-associated regenerative failure.

CBFβ-SMMHC creates aberrant megakaryocyte-erythroid progenitors prone to leukemia initiation in mice

Acute myeloid leukemia (AML) arises through multistep clonal evolution characterized by stepwise accumulation of successive alterations affecting the homeostasis of differentiation, proliferation, self-renewal, and survival programs. The persistence and dynamic clonal evolution of leukemia-initiating cells and preleukemic stem cells during disease progression and treatment are thought to contribute to disease relapse and poor outcome. Inv(16)(p13q22) or t(16;16)(p13.1;q22), one of the most common cytogenetic abnormalities in AML, leads to expression of a fusion protein CBFβ-SMMHC (CM) known to disrupt myeloid and lymphoid differentiation. Anemia is often observed in AML but is presumed to be a secondary consequence of leukemic clonal expansion. Here, we show that CM expression induces marked deficiencies in erythroid lineage differentiation and early preleukemic expansion of a phenotypic pre-megakaryocyte/erythrocyte (Pre-Meg/E) progenitor population. Using dual-fluorescence reporter mice in lineage tracking and repopulation assays, we show that CM expression cell autonomously causes expansion of abnormal Pre-Meg/E progenitors with compromised erythroid specification and differentiation capacity. The preleukemic Pre-Meg/Es display dysregulated erythroid and megakaryocytic fate-determining factors including increased Spi-1, Gata2, and Gfi1b and reduced Zfpm1, Pf4, Vwf, and Mpl expression. Furthermore, these abnormal preleukemic Pre-Meg/Es have enhanced stress resistance and are prone to leukemia initiation upon acquiring cooperative signals. This study reveals that the leukemogenic CM fusion protein disrupts adult erythropoiesis and creates stress-resistant preleukemic Pre-Meg/E progenitors predisposed to malignant transformation. Abnormality in Meg/E or erythroid progenitors could potentially be considered an early predictive risk factor for leukemia evolution.

Merestinib blocks Mnk kinase activity in acute myeloid leukemia progenitors and exhibits antileukemic effects in vitro and in vivo

Mitogen-activated protein kinase interacting protein kinases (Mnks) play important roles in the development and progression of acute myeloid leukemia (AML) by regulating eukaryotic translation initiation factor 4E (eIF4E) activation. Inhibiting Mnk1/2-induced phosphorylation of eIF4E may represent a unique approach for the treatment of AML. We provide evidence for antileukemic effects of merestinib, an orally bioavailable multikinase inhibitor with suppressive effects on Mnk activity. Our studies show that merestinib effectively blocks eIF4E phosphorylation in AML cells and suppresses primitive leukemic progenitors from AML patients in vitro and in an AML xenograft model in vivo. Our findings provide evidence for potent preclinical antileukemic properties of merestinib and support its clinical development for the treatment of patients with AML.

Small-Molecule Targeting of BET Proteins in Cancer

BET proteins have recently become recognized for their role in a broad range of cancers and are defined by the presence of two acetyl-histone reading bromodomains and an ET domain. This family of proteins includes BRD2, BRD3, BRD4, and BRDT. BRD4 is the most-studied BET protein in cancer, and normally serves as an epigenetic reader that links active chromatin marks to transcriptional elongation through activation of RNA polymerase II. The role of BRD3 and BRD4 first became known in cancer as mutant oncoproteins fused to the p300-recruiting NUT protein in a rare aggressive subtype of squamous cell cancer known as NUT midline carcinoma (NMC). BET inhibitors are acetyl-histone mimetics that specifically bind BET bromodomains, competitively inhibiting its engagement with chromatin. The antineoplastic effects of BET inhibitors were first demonstrated in NMC and have since been shown to be effective at inhibiting the growth of many different cancers, particularly acute leukemia. BET inhibitors have also been instrumental as tool compounds that have demonstrated the key role of BRD4 in driving NMC and non-NMC cancer growth. Many clinical trials enrolling patients with hematologic and solid tumors are ongoing, with encouraging preliminary findings. BET proteins BRD2, BRD3, and BRD4 are expressed in nearly all cells of the body, so there are concerns of toxicity with BET inhibitors, as well as the development of resistance. Toxicity and resistance may be overcome by combining BET inhibitors with other targeted inhibitors, or through the use of novel BET inhibitor derivatives.

Dual targeting of eIF4E by blocking MNK and mTOR pathways in leukemia

Dysregulation of mRNA translation leads to aberrant activation of cellular pathways that promote expansion and survival of leukemic clones. A key element of the initiation translation complex is eIF4E (eukaryotic translation initiation factor 4E). The mitogen-activated protein kinase (MAPK) and mammalian target of rapamycin (mTOR) pathways play important roles in the regulation of eIF4E expression and downstream functional outcomes. Mitogen-activated protein kinase interacting protein kinases (Mnks) control translation by phosphorylation of eIF4E, whereas the mTOR kinase phosphorylates/de-activates the eIF4E inhibitor, 4E-BP1, to release translational repression. Both pathways are often abnormally activated in leukemia cells and promote cell survival events by controlling expression of oncogenic proteins. Targeting these pathways may provide approaches to avoid aberrant proliferation and neoplastic transformation.

Monocyte-macrophage differentiation of acute myeloid leukemia cell lines by small molecules identified through interrogation of the Connectivity Map database

The transcription factor C/EBPα is required for granulocytic differentiation of normal myeloid progenitors and is frequently inactivated in acute myeloid leukemia (AML) cells. Ectopic expression of C/EBPα in AML cells suppresses proliferation and induces differentiation suggesting that restoring C/EBPα expression/activity in AML cells could be therapeutically useful. Unfortunately, current approaches of gene or protein delivery in leukemic cells are unsatisfactory. However, "drug repurposing" is becoming a very attractive strategy to identify potential new uses for existing drugs. In this study, we assessed the biological effects of candidate C/EBPα-mimetics identified by interrogation of the Connectivity Map database. We found that amantadine, an antiviral and anti-Parkinson agent, induced a monocyte-macrophage-like differentiation of HL60, U937, Kasumi-1 myeloid leukemia cell lines, as indicated by morphology and differentiation antigen expression, when used in combination with suboptimal concentration of all trans retinoic acid (ATRA) or Vit D3. The effect of amantadine depends, in part, on increased activity of the vitamin D receptor (VDR), since it induced VDR expression and amantadine-dependent monocyte-macrophage differentiation of HL60 cells was blocked by expression of dominant-negative VDR. These results reveal a new function for amantadine and support the concept that screening of the Connectivity Map database can identify small molecules that mimic the effect of transcription factors required for myelo-monocytic differentiation.

Gene mutation patterns in patients with minimally differentiated acute myeloid leukemia

Minimally differentiated acute myeloid leukemia (AML-M0) is a rare subtype of AML with poor prognosis. Although genetic alterations are increasingly reported in AML, the gene mutations have not been comprehensively studied in AML-M0. We aimed to examine a wide spectrum of gene mutations in patients with AML-M0 to determine their clinical relevance. Twenty gene mutations including class I, class II, class III of epigenetic regulators (IDH1, IDH2, TET2, DNMT3A, MLL-PTD, ASXL1, and EZH2), and class IV (tumor suppressor genes) were analyzed in 67 patients with AML-M0. Mutational analysis was performed with polymerase chain reaction–based assays followed by direct sequencing. The most frequent gene mutations from our data were FLT3-ITD/FLT3-TKD (28.4%), followed by mutations in IDH1/IDH2 (28.8%), RUNX1 (23.9%), N-RAS/K-RAS (12.3%), TET2 (8.2%), DNMT3A (8.1%), MLL-PTD (7.8%), and ASXL1 (6.3%). Seventy-nine percent (53/67) of patients had at least one gene mutation. Class I genes (49.3%) were the most common mutated genes, which were mutually exclusive. Class III genes of epigenetic regulators were also frequent (43.9%). In multivariate analysis, old age [hazard ratio (HR) 1.029, 95% confidence interval (CI) 1.013-1.044, P = .001) was the independent adverse factor for overall survival, and RUNX1 mutation (HR 2.326, 95% CI 0.978-5.533, P = .056) had a trend toward inferior survival. In conclusion, our study showed a high frequency of FLT3, RUNX1, and IDH mutations in AML-M0, suggesting that these mutations played a role in the pathogenesis and served as potential therapeutic targets in this rare and unfavorable subtype of AML.

Normal hematopoietic stem cells within the AML bone marrow have a distinct and higher ALDH activity level than co-existing leukemic stem cells

Persistence of leukemic stem cells (LSC) after chemotherapy is thought to be responsible for relapse and prevents the curative treatment of acute myeloid leukemia (AML) patients. LSC and normal hematopoietic stem cells (HSC) share many characteristics and co-exist in the bone marrow of AML patients. For the development of successful LSC-targeted therapy, enabling eradication of LSC while sparing HSC, the identification of differences between LSC and HSC residing within the AML bone marrow is crucial. For identification of these LSC targets, as well as for AML LSC characterization, discrimination between LSC and HSC within the AML bone marrow is imperative. Here we show that normal CD34+CD38– HSC present in AML bone marrow, identified by their lack of aberrant immunophenotypic and molecular marker expression and low scatter properties, are a distinct sub-population of cells with high ALDH activity (ALDH^bright). The ALDH^bright compartment contains, besides normal HSC, more differentiated, normal CD34+CD38+ progenitors. Furthermore, we show that in CD34-negative AML, containing solely normal CD34+ cells, LSC are CD34– and ALDH^low. In CD34-positive AML, LSC are also ALDH^low but can be either CD34+ or CD34–. In conclusion, although malignant AML blasts have varying ALDH activity, a common feature of all AML cases is that LSC have lower ALDH activity than the CD34+CD38– HSC that co-exist with these LSC in the AML bone marrow. Our findings form the basis for combined functionally and immunophenotypically based identification and purification of LSC and HSC within the AML bone marrow, aiming at development of highly specific anti-LSC therapy.

Children's Oncology Group's 2013 blueprint for research: acute myeloid leukemia

For the 365 children diagnosed with acute myeloid leukemia in the US annually, 5-year survival for patients on COG trials with low, intermediate, and high risk disease is 83%, 62%, and 23%, respectively. Recent advances include improved therapeutic stratification, improved survival with dose intensification, and further elucidation of the heterogeneity specific to childhood AML. These discoveries now guide current strategy incorporating targeted agents to pathways specific to childhood AML as well as evaluating methods to increase the sensitivity of the leukemic stem cell, first in Phase II feasibility trials followed by Phase III efficacy trials of the most promising agents. Acute myeloid leukemia in children, though with similar subgroups to adults, remains uniquely different based upon quite different prevalence of subtypes as well as overall response to therapy. The Children's Oncology Group's research agenda builds upon earlier efforts to better elucidate the leukemogenic steps distinct to childhood AML in order to more scientifically develop and test novel therapeutic approaches to the treatment and ultimate cure for children with this disorder. Pediatr Blood Cancer 2013; 60: 964-971. © 2012 Wiley Periodicals, Inc.

Notch pathway activation targets AML-initiating cell homeostasis and differentiation

Notch behaves as a tumor suppressor in AML, and Notch activation induces cell cycle arrest, differentiation, and apoptosis of AML-initiating cells.

Notch signaling pathway activation is known to contribute to the pathogenesis of a spectrum of human malignancies, including T cell leukemia. However, recent studies have implicated the Notch pathway as a tumor suppressor in myeloproliferative neoplasms and several solid tumors. Here we report a novel tumor suppressor role for Notch signaling in acute myeloid leukemia (AML) and demonstrate that Notch pathway activation could represent a therapeutic strategy in this disease. We show that Notch signaling is silenced in human AML samples, as well as in AML-initiating cells in an animal model of the disease. In vivo activation of Notch signaling using genetic Notch gain of function models or in vitro using synthetic Notch ligand induces rapid cell cycle arrest, differentiation, and apoptosis of AML-initiating cells. Moreover, we demonstrate that Notch inactivation cooperates in vivo with loss of the myeloid tumor suppressor Tet2 to induce AML-like disease. These data demonstrate a novel tumor suppressor role for Notch signaling in AML and elucidate the potential therapeutic use of Notch receptor agonists in the treatment of this devastating leukemia.

Immunologic consequences of chemotherapy for acute myeloid leukemia

There are few data characterizing the immunologic consequences of chemotherapy for acute myeloid leukemia (AML) and almost nothing is known about the effects of chemotherapy in a pediatric AML cohort. We identified T-cell subsets, B-cell subsets, and used Enzyme-linked immunosorbent spot analyses to define the function of T cells and B cells in 7 pediatric patients with AML on chemotherapy. The data show that the effects of chemotherapy disproportionately target the B cell and depletion of B cells is associated with impaired responses to the inactivated influenza vaccine. Diminished T-cell numbers were also observed although the magnitude of the effect was less than what was seen for B cells. Furthermore, measures of T-cell function were largely intact. We conclude that humoral immunity is significantly affected by chemotherapy for AML.

PML-RARα co-operates with Sox4 in acute myeloid leukemia development in mice

Acute promyelocytic leukemia is characterized by a chromosomal translocation involving the retinoic acid receptor alpha gene. To identify co-operating pathways to leukemogenesis, we crossed MRP8-PML/RARA transgenic mice with BXH-2 mice which harbor an endogenous murine leukemia virus that causes acute myeloid leukemia. Approximately half of the leukemias that arose in this cross showed features of acute promyelocytic leukemia. We identified 22 proviral insertion sites in acute promyelocytic-like leukemias and focused our analysis on insertion at Sox4, a HMG box transcription factor. Using a transplant model, co-operation between PML-RARα and Sox4 was confirmed with increased penetrance and reduced latency of disease. Interestingly, karyotypic analysis revealed cytogenetic changes suggesting that the factors combined to initiate but not complete leukemic transformation. The cooperation between these transcription factors is consistent with the paradigm of multiple routes to the disease and reinforces the concept that transcription factor networks are important therapeutic targets in myeloid leukemias.

Analysis of Chromosomal Aberrations and FLT3 gene Mutations in Childhood Acute Myelogenous Leukemia Patients

Objective: To identify the well-known common translocations and FLT3 mutations in childhood acute myelogenousleukemia (AML) patients in Turkey.

Material and Methods: The study included 50 newly diagnosed patients in which t(15;17), t(8;21), and inv(16)chromosomal translocations were identified using real-time PCR and FLT3 gene mutations were identified via direct PCR amplification PCR-RE analysis.

Results: In all, t(15;17) chromosomal aberrations were observed in 4 patients (8.0%), t(8;21) chromosomal aberrationswere observed in 12 patients (24.0%), inv(16) chromosomal aberrations were observed in 3 patients (6.0%), and FLT3-ITD mutations were observed in 2 patients (4.0%); FLT3-D835 point mutation heterozygosity was observed in only 1patient (2.0%) patient.

Conclusion: Despite of the known literature, a patient with FLT3-ITD and FLT3-D835 double mutation shows a bettersurvival and this might be due to the complementation effect of the t(15;17) translocation. The reportedmutation ratein this article (4%) of FLT3 gene seems to be one of the first results for Turkish population.

Prognostic impact of NPM1 mutations in Serbian adult patients with acute myeloid leukemia

Based on current findings, the presence of NPM1 mutations in acute myeloid leukemia (AML) patients is associated with an increased probability of complete remission (CR) and better overall survival (OS). We determined the incidence and prognostic relevance of NPM1 mutations, their association with FLT3 and IDH mutations, and other clinical characteristics in Serbian adult AML patients. Samples from 111 adult de novo AML patients, including 73 AML cases with a normal karyotype (NK-AML), were studied. NPM1, FLT3, and IDH mutations were detected by PCR and direct sequencing. NPM1 mutations were detected in 22.5% of patients. The presence of NPM1 mutations predicted a low CR rate and shorter OS. NPM1 mutations showed an association with both FLT3 and IDH mutations. Survival analysis based on NPM1/FLT3 mutational status revealed a lower OS for NPM1(+)/FLT3(-) compared to the NPM1(-)/FLT3(-) group in NK-AML patients. The lack of impact or unfavorable prognostic effect of NPM1 mutations found in this study can be assigned to a small cohort of analyzed AML patients, as can the presence of FLT3 and IDH mutations or other genetic lesions that cooperate with NPM1 mutations influencing prognosis.

AML1-ETO driven acute leukemia: insights into pathogenesis and potential therapeutic approaches

The AML1-ETO fusion transcription factor is generated by the t(8;21) translocation, which is present in approximately 4%-12% of adult and 12%-30% of pediatric acute myeloid leukemia (AML) patients. Both human and mouse models of AML have demonstrated that AML1-ETO is insufficient for leukemogenesis in the absence of secondary events. In this review, we discuss the pathogenetic insights that have been gained from identifying the various events that can cooperate with AML1-ETO to induce AML in vivo. We also discuss potential therapeutic strategies for t(8;21) positive AML that involve targeting the fusion protein itself, the proteins that bind to it, or the genes that it regulates. Recently published studies suggest that a targeted therapy for t(8;21) positive AML is feasible and may be coming sometime soon.

Differentially expressed miRNAs in cytogenetic and molecular subtypes of pediatric acute myeloid leukemia

BACKGROUND

miRNAs regulate gene expression, and thus play an important role in critical cellular processes. Aberrant miRNA expression patterns have been found in various types of cancer. So far, information about the expression of miRNAs in pediatric acute myeloid leukemia is limited.

PROCEDURE

We studied expression of miR-29a, -155, -196a, and -196b by stem-loop based RT-qPCR in 82 pediatric acute myeloid leukemia patients selected to represent relevant cytogenetic and molecular subgroups.

RESULTS

High miR-196a and -b expression was observed in patients carrying MLL gene rearrangements (P < 0.001), NPM1 mutations (P < 0.001), or FLT3-ITD in a cytogenetically normal background (P ≤ 0.02), compared to all other patients. In contrast, CEBPA mutated cases had a low expression of miR-196a and -b (P ≤ 0.001). Expression of miR-196a and -b was correlated with expression of neighboring HOXA and HOXB genes (Spearman's r = 0.46-0.82, P < 0.01). Expression of miR-155 was not related to cytogenetic features but high expression of miR-155 was observed in FLT3-ITD (P = 0.001) and NPM1-mutated cases (P = 0.04). Lower miR-29a expression was mainly observed in MLL-rearranged pediatric acute myeloid leukemia, specifically in cases carrying t(10;11) (P < 0.001).

CONCLUSIONS

We show aberrant expression of specific miRNAs in clinically relevant cytogenetic and molecular subgroups of pediatric acute myeloid leukemia, suggesting a role for these miRNAs in the underlying biology in these specific subgroups.

Increased dosage of the chromosome 21 ortholog Dyrk1a promotes megakaryoblastic leukemia in a murine model of Down syndrome

Individuals with Down syndrome (DS; also known as trisomy 21) have a markedly increased risk of leukemia in childhood but a decreased risk of solid tumors in adulthood. Acquired mutations in the transcription factor-encoding GATA1 gene are observed in nearly all individuals with DS who are born with transient myeloproliferative disorder (TMD), a clonal preleukemia, and/or who develop acute megakaryoblastic leukemia (AMKL). Individuals who do not have DS but bear germline GATA1 mutations analogous to those detected in individuals with TMD and DS-AMKL are not predisposed to leukemia. To better understand the functional contribution of trisomy 21 to leukemogenesis, we used mouse and human cell models of DS to reproduce the multistep pathogenesis of DS-AMKL and to identify chromosome 21 genes that promote megakaryoblastic leukemia in children with DS. Our results revealed that trisomy for only 33 orthologs of human chromosome 21 (Hsa21) genes was sufficient to cooperate with GATA1 mutations to initiate megakaryoblastic leukemia in vivo. Furthermore, through a functional screening of the trisomic genes, we demonstrated that DYRK1A, which encodes dual-specificity tyrosine-(Y)-phosphorylation-regulated kinase 1A, was a potent megakaryoblastic tumor-promoting gene that contributed to leukemogenesis through dysregulation of nuclear factor of activated T cells (NFAT) activation. Given that calcineurin/NFAT pathway inhibition has been implicated in the decreased tumor incidence in adults with DS, our results show that the same pathway can be both proleukemic in children and antitumorigenic in adults.

AKT/FOXO signaling enforces reversible differentiation blockade in myeloid leukemias

AKT activation is associated with many malignancies, where AKT acts, in part, by inhibiting FOXO tumor suppressors. We show a converse role for AKT/FOXOs in acute myeloid leukemia (AML). Rather than decreased FOXO activity, we observed that FOXOs are active in ∼40% of AML patient samples regardless of genetic subtype. We also observe this activity in human MLL-AF9 leukemia allele-induced AML in mice, where either activation of Akt or compound deletion of FoxO1/3/4 reduced leukemic cell growth, with the latter markedly diminishing leukemia-initiating cell (LIC) function in vivo and improving animal survival. FOXO inhibition resulted in myeloid maturation and subsequent AML cell death. FOXO activation inversely correlated with JNK/c-JUN signaling, and leukemic cells resistant to FOXO inhibition responded to JNK inhibition. These data reveal a molecular role for AKT/FOXO and JNK/c-JUN in maintaining a differentiation blockade that can be targeted to inhibit leukemias with a range of genetic lesions.

High BRE expression predicts favorable outcome in adult acute myeloid leukemia, in particular among MLL-AF9-positive patients

Aberrations in protein ubiquitination have recently been identified in the pathogenesis of acute myeloid leukemia (AML). We studied whether expression changes of more than 1600 ubiquitination related genes correlated with clinical outcome in 525 adult AML patients. High expression of one of these genes, BRE, was observed in 3% of the cases and predicted favorable prognosis independently of known prognostic factors (5-year overall survival: 57%). Remarkably, unsupervised expression profiling showed that 86% of high BRE-expressing patients were confined to a previously unrecognized cluster. High BRE expression was mutually exclusive with FLT3 ITD, CEBPA, IDH1, and IDH2 mutations, EVI1 overexpression, and favorable karyotypes. In contrast, high BRE expression co-occurred strongly with FAB M5 morphology and MLL-AF9 fusions. Within the group of MLL-AF9-positive patients, high BRE expression predicted superior survival, while normal BRE expression predicted extremely poor survival (5-year overall survival of 80% vs 0%, respectively, P = .0002). Both the co-occurrence of high BRE expression with MLL-AF9 and its prognostic impact were confirmed in an independent cohort of 436 AML patients. Thus, high BRE expression defines a novel subtype of adult AML characterized by a favorable prognosis. This work contributes to improved risk stratification in AML, especially among MLL-AF9-positive patients.

Two types of C/EBPα mutations play distinct but collaborative roles in leukemogenesis: lessons from clinical data and BMT models

Two types of mutations of a transcription factor CCAAT-enhancer binding protein α (C/EBPα) are found in leukemic cells of 5%-14% of acute myeloid leukemia (AML) patients: N-terminal mutations expressing dominant negative p30 and C-terminal mutations in the basic leucine zipper domain. Our results showed that a mutation of C/EBPα in one allele was observed in AML after myelodysplastic syndrome, while the 2 alleles are mutated in de novo AML. Unlike an N-terminal frame-shift mutant (C/EBPα-Nm)–transduced cells, a C-terminal mutant (C/EBPα-Cm)–transduced cells alone induced AML with leukopenia in mice 4-12 months after bone marrow transplantation. Coexpression of both mutants induced AML with marked leukocytosis with shorter latencies. Interestingly, C/EBPα-Cm collaborated with an Flt3-activating mutant Flt3-ITD in inducing AML. Moreover, C/EBPα-Cm strongly blocked myeloid differentiation of 32Dcl3 cells, suggesting its class II mutation-like role in leukemogenesis. Although C/EBPα-Cm failed to inhibit transcriptional activity of wild-type C/EBPα, it suppressed the synergistic effect between C/EBPα and PU.1. On the other hand, C/EBPα-Nm inhibited C/EBPα activation in the absence of PU.1, despite low expression levels of p30 protein generated by C/EBPα-Nm. Thus, 2 types of C/EBPα mutations are implicated in leukemo-genesis, involving different and cooperating molecular mechanisms.

Expression profiling of cytogenetically normal acute myeloid leukemia identifies microRNAs that target genes involved in monocytic differentiation

MicroRNAs are short ribonucleic acids (RNAs) that play an important role in many aspects of cellular biology such as differentiation and apoptosis, due to their role in the regulation of gene expression. Using microRNA microarrays, we characterized the microRNA gene expression of 27 patients with acute myeloid leukemia (AML) with normal cytogenetics, focusing on the microRNAs differentially expressed between the M1 and M5 French-American-British (FAB) subtypes. An accurate delineation of these two AML entities was observed based on the expression of 12 microRNAs. We hypothesized that these microRNAs may potentially be involved in the differentiation block of M1 blasts and consequently monocytic differentiation. Using publically available mRNA data and microRNA target prediction software, we identified several key myeloid factors that may be targeted by our candidate microRNAs. The expression changes of the candidate microRNAs during monocytic differentiation of AML cell lines treated with Vitamin D and phorbol 12-myristate 13-acetate were examined. All six candidate microRNAs were significantly down-regulated over the time course by quantitative reverse transcriptase polymerase chain reaction suggesting a link between these microRNAs and monocytic differentiation. To further characterize these microRNAs, we confirmed by luciferase assays that these microRNA target several key myeloid factors such as MAFB, IRF8, and KLF4 identifying a possible mechanism for the control of differentiation by these microRNAs.

Molecular pathogenesis of acute myeloid leukemia: a diverse disease with new perspectives

Acute myeloid leukemia (AML) is a very heterogeneous neoplasm of the hematopoietic stem cell. Despite important achievements in the treatment of AML, the long term survival of patients with the disease remains poor. Understanding the pathogenesis of AML better is crucial for finding new treatment approaches. During AML development, hematopoietic precursor cells undergo clonal transformation in a multistep process through acquisition of chromosomal rearrangements and/or different gene mutations. Over recent years, novel gene mutations have been found in patients with AML. These mutations can be divided into two important categories, class I mutations that confer a proliferation advantage and class II mutations that inhibit myeloid differentiation. Screening for some of these mutations is now part of the initial diagnostic workup in newly diagnosed AML patients. Information about the mutation status of specific genes is useful for risk-stratification, minimal residual disease (MRD) monitoring and increasingly also for targeted therapy, especially for patients with cytogenetically normal AML (CN-AML). Besides chromosomal rearrangements and gene mutations, epigenetic regulation of genes - meaning changes in gene expression by mechanisms other than changes in the underlying DNA sequence - also represents an important mechanism of leukemogenesis. This article reviews some of the most common mutations in CN-AML and gives a perspective of the translation of these discoveries from bench to bedside.

Acute myeloid leukemia

Acute myeloid leukemia (AML) is a heterogeneous group of leukemias that result from clonal transformation of hematopoietic precursors through the acquisition of chromosomal rearrangements and multiple gene mutations. As a result of highly collaborative clinical research by pediatric cooperative cancer groups worldwide, disease-free survival has improved significantly during the past 3 decades. Further improvements in outcomes of children who have AML probably will reflect continued progress in understanding the biology of AML and the concomitant development of new molecularly targeted agents for use in combination with conventional chemotherapy drugs.

Myeloid-specific inactivation of p15Ink4b results in monocytosis and predisposition to myeloid leukemia

Inactivation of p15INK4b, an inhibitor of cyclin-dependent kinases, through DNA methylation is one of the most common epigenetic abnormalities in myeloid leukemia. Although this suggests a key role for this protein in myeloid disease suppression, experimental evidence to support this has not been reported. To address whether this event is critical for premalignant myeloid disorders and leukemia development, mice were generated that have loss of p15Ink4b specifically in myeloid cells. The p15Ink4b(fl/fl)-LysMcre mice develop nonreactive monocytosis in the peripheral blood accompanied by increased numbers of myeloid and monocytic cells in the bone marrow resembling the myeloproliferative form of chronic myelomonocytic leukemia. Spontaneous progression from chronic disease to acute leukemia was not observed. Nevertheless, MOL4070LTR retrovirus integrations provided cooperative genetic mutations resulting in a high frequency of myeloid leukemia in knockout mice. Two common retrovirus insertion sites near c-myb and Sox4 genes were identified, and their transcript up-regulated in leukemia, suggesting a collaborative role of their protein products with p15Ink4b-deficiency in promoting malignant disease. This new animal model demonstrates experimentally that p15Ink4b is a tumor suppressor for myeloid leukemia, and its loss may play an active role in the establishment of preleukemic conditions.

Which AML subsets benefit from leukemic cell priming during chemotherapy? Long-term analysis of the ALFA-9802 GM-CSF study

BACKGROUND

: Priming with granulocytic hematopoietic growth factors may modulate cell cycle kinetics of leukemic cells and render them more susceptible to phase-specific chemotherapeutic agents. In a first report, we have shown that priming with granulocyte-macrophage colony-stimulating factor (GM-CSF) may enhance complete remission (CR) rate and event-free survival (EFS) in younger adults with acute myeloid leukemia (AML).

METHODS

: In this randomized trial, 259 patients with AML were randomized at baseline to receive or not receive GM-CSF concurrently with all cycles of chemotherapy. The effects of GM-CSF on survival were reported herein with a long-term follow-up and studied according to distinct biological subgroups defined on cytogenetics and molecular markers.

RESULTS

: The EFS rate was better in the GM-CSF group (43% vs 34%; P = .04). GM-CSF did not improve the outcome in patients from good risk subgroups, while patients from poor risk subgroups benefited from GM-CSF therapy. In this population, the difference in terms of EFS probability was mainly observed in patients with high initial white blood cell count and in those with FLT3-ITD or MLL rearrangement. When combining these 2 molecular abnormalities for comparison of the effect of GM-CSF priming, the difference in terms of EFS was highly significant (5-year EFS, 39% with GM-CSF vs 8% without GM-CSF; P = .007).

CONCLUSIONS

: Sensitization of leukemic cells and their progenitors by GM-CSF appears as a plausible strategy for improving the outcome of patients with newly diagnosed AML. Patients with poor-prognosis FLT3-ITD or MLL rearrangement might be a good target population to further investigate priming strategies. Cancer 2010. (c) 2010 American Cancer Society.

Genome wide molecular analysis of minimally differentiated acute myeloid leukemia

BACKGROUND

Minimally differentiated acute myeloid leukemia is heterogeneous in karyotype and is defined by immature morphological and molecular characteristics. This originally French-American-British classification is still used in the new World Health Organization classification when other criteria are not met. Apart from RUNX1 mutation, no characteristic molecular aberrations are recognized.

DESIGN AND METHODS

We performed whole genome single nucleotide polymorphism analysis and extensive molecular analysis in a cohort of 52 patients with minimally differentiated acute myeloid leukemia.

RESULTS

Many recurring and potentially relevant regions of loss of heterozygosity were revealed. These point towards a variety of candidate genes that could contribute to the pathogenesis of minimally differentiated acute myeloid leukemia, including the tumor suppressor genes TP53 and NF1, and reinforced the importance of RUNX1 in this leukemia. Furthermore, for the first time in this minimally differentiated form of leukemia we detected mutations in the transactivation domain of RUNX1. Mutations in other acute myeloid leukemia associated transcriptions factors were infrequent. In contrast, FLT3, RAS, PTPN11 and JAK2 were often mutated. Irrespective of the RUNX1 mutation status, our results show that RAS signaling is the most important pathway for proliferation in minimally differentiated acute myeloid leukemia. Importantly, we found that high terminal deoxynucleotidyl transferase expression is closely associated with RUNX1 mutation, which could allow an easier diagnosis of RUNX1 mutation in this hematologic malignancy.

CONCLUSIONS

Our results suggest that in patients without RUNX1 mutation, several other molecular aberrations, separately or in combination, contribute to a common minimally differentiated phenotype.

Cell-cycle regulation and dynamics of cytoplasmic compartments containing the promyelocytic leukemia protein and nucleoporins

Nucleoporins and the promyelocytic leukemia protein (PML) represent structural entities of nuclear pore complexes and PML nuclear bodies, respectively. In addition, these proteins might function in a common biological mechanism, because at least two different nucleoporins, Nup98 and Nup214, as well as PML, can become aberrantly expressed as oncogenic fusion proteins in acute myeloid leukemia (AML) cells. Here we show that PML and nucleoporins become directed to common cytoplasmic compartments during the mitosis-to-G1 transition of the cell cycle. These protein assemblies, which we have termed CyPNs (cytoplasmic assemblies of PML and nucleoporins), move on the microtubular network and become stably connected to the nuclear membrane once contact with the nucleus has been made. The ability of PML to target CyPNs depends on its nuclear localization signal, and loss of PML causes an increase in cytoplasmic-bound versus nuclear-membrane-bound nucleoporins. CyPNs are also targeted by the acute promyelocytic leukemia (APL) fusion protein PML-RARalpha and can be readily detected within the APL cell line NB4. These results provide insight into a dynamic pool of cytoplasmic nucleoporins that form a complex with the tumor suppressor protein PML during the G1 phase of the cell cycle.

Nuclear factor-kappaB modulation in patients undergoing induction chemotherapy for acute myelogenous leukemia

PURPOSE

Nuclear factor-kappaB (NF-kappaB) is constitutively expressed in many acute myelogenous leukemia (AML) cells and AML stem cells. Ex vivo treatment of AML cells with inhibitors of NF-kappaB results in diminished AML cell survival and enhances the cytotoxic effects of chemotherapeutic agents. The purpose of this study was to determine if standard anti-inflammatory agents modulate AML cell nuclear NF-kappaB when administered in conjunction with induction chemotherapy.

EXPERIMENTAL DESIGN

Patients with newly diagnosed AML were treated with dexamethasone, choline magnesium trisalicylate, or both for 24 hours prior to and 24 hours following initiation of standard induction chemotherapy. AML cell nuclear NF-kappaB was measured at baseline, 24, and 48 hours.

RESULTS

Choline magnesium trisalicylate +/- dexamethasone decreased nuclear NF-kappaB, whereas dexamethasone alone was associated with an increase in nuclear NF-kappaB in AML cells.

CONCLUSIONS

These results show the feasibility of NF-kappaB modulation in conjunction with induction chemotherapy for patients with AML using inexpensive readily available medications. A follow-up study to determine the effects of NF-kappaB modulation on clinical end points is warranted.

ASB2 targets filamins A and B to proteasomal degradation

The ordered series of proliferation and differentiation from hematopoietic progenitor cells is disrupted in leukemia, resulting in arrest of differentiation at immature proliferative stages. Characterizing the molecular basis of hematopoietic differentiation is therefore important for understanding and treating disease. Retinoic acid induces expression of ankyrin repeat-containing protein with a suppressor of cytokine signaling box 2 (ASB2) in acute promyelocytic leukemia cells, and ASB2 expression inhibits growth and promotes commitment, recapitulating an early step critical for differentiation. ASB2 is the specificity subunit of an E3 ubiquitin ligase complex and is proposed to exert its effects by regulating the turnover of specific proteins; however, no ASB2 substrates had been identified. Here, we report that ASB2 targets the actin-binding proteins filamin A and B for proteasomal degradation. Knockdown of endogenous ASB2 in leukemia cells delays retinoic acid-induced differentiation and filamin degradation; conversely, ASB2 expression in leukemia cells induces filamin degradation. ASB2 expression inhibits cell spreading, and this effect is recapitulated by knocking down both filamin A and filamin B. Thus, we suggest that ASB2 may regulate hematopoietic cell differentiation by modulating cell spreading and actin remodeling through targeting of filamins for degradation.